The International Bone Marrow Transplant Registry (IBMTR) is a collaborative study group that has been conducting research for the past 20 years in an effort to improve the safety and success of bone marrow transplantation for the treatment of a variety of otherwise largely incurable diseases. At present nearly 200 (more than 75% of all) transplant teams in the US and abroad voluntarily contribute detailed information regarding their consecutive transplant cases to the IBMTR on uniform reporting forms. Data for more than 10,000 recipients of allogeneic and syngeneic transplants are presently stored in the IBMTR database. Reporting forms are being prepared and data collection for autologous bone marrow transplants will be initiated in 1990. In this five-year Program Project renewal application, the Advisory Committees of the IBMTR and the North American Autologous Bone Marrow Transplant Registry (NAABMTR) request support for a statistical core component that is required by and shared solely within the proposed research program. Support also is requested to conduct studies designed to address key questions that would be difficult or impossible for single institutions to undertake but can be investigated using pooled data from multiple centers. Project I is focused on critical but unresolved issues in allogeneic bone marrow transplantation for both common and rare diseases such as leukemia, myelodysplastic syndromes and Fanconi anemia. Project II addresses immunogenetic and management problems in allogeneic bone marrow transplantation such as HLA-matched and mismatched related and unrelated donor selection, graft-versus-host disease, graft-versus- leukemia reactions and late effects of bone marrow transplantation. Project III examines critical but unresolved issues in autologous bone marrow transplants for acute leukemia, lymphoma, neuroblastoma and breast cancer.